Separation of hydrocarbons by dual solvent extraction



United States Patent SEPARATION OF HYDROCARBONS BY DUAL SOLVENT EXTRACTION Raymond N. Fleck, Whittier, and Carlyle G. Wight, Fullerton, Calif., assignors to Union Oil Company of California, Los Angeles, Calif., a corporation of California Filed Apr. 18, 1957, Ser. No. 653,699

16 Claims. 01. 260-676) This invention relates to methods for resolving hydrocarbon mixtures whereby pure individual parafiins, naphthenes, aromatics, and/or olefins may be obtained. The salient feature of the process involves subjecting narrow boiling range hydrocarbon mixtures to solvent extraction in the presence of two substantially immiscible solvents. The more highly paraflinic component is selectively dissolved in the primary solvent, and the less paraflinic component by the secondary solvent. The primary solvent is a perfluoro compound, and the secondary solvent may be a conventional polar organic compound of the general class known in the art to be selective for carbon-rich hydrocarbons as opposed to relatively hydrogen-rich hydrocarbons.

It has been found that hydrocarbons whose alkyl carbon skeleton is relatively exposed, as in a straightchain, are less soluble in the primary solvent than chemically similar hydrocarbons whose alkyl carbon skeleton is relatively more enclosed by hydrogen atoms, as in a branched-chain. The ditferencm in solubility however are relatively small, and hence solvent extraction with the primary solvent alone is impractical. It has been discovered, however, that when the extraction is performed in the presence of the secondary solvent, the separation factor is greatly increased, and effective separation of isomeric hydrocarbons becomes possible by solvent extraction, a result not heretofore obtainable in practice.

It is therefore an object of the invention to provide solvent extraction methods for separating isomeric parafiins, isomeric naphthenes, isomeric olefins, isomeric alkaryl hydrocarbons, or combinations thereof. A broader object is to provide solvent extraction methods for resolving hydrocarbon mixtures wherein the components differ from each other only slightly in degree of parafiinicity. Another object is to provide novel dualsolvent systems of optimum efliciency for effecting such separations. A further object is to provide novel techniques for utilizing dual-solvent systems for maximum efliciency and economy. These and other objectives are achieved in accordance with the present invention, as will be apparent from the following description.

It is known in the art that certain solvents, e.g. aniline, diethylene glycol, phenol, etc., exhibit a selective solvent action for hydrocarbons in which the carbon/hydrogen ratio is high (as in aromatics) as compared to hydrocarbons wherein the carbon/hydrogen ratio is relatively low (as in paraflins). Generally the various hydrocarbon types exhibit solubilities in these solvents in the decreasing order: aromatics, polyolefins, mono-olefins, naphthenes, paraflins. Consequently, like-boiling members from any two of the foregoing classes may be separated by solvent extraction with such conventional solvents.

The process of the present invention can also efiect such separations, but differs from the foregoing in that the hydrocarbons separated need display no difference l iC in carbon/hydrogen ratio. It is believed that no pre viously known solvent extraction methods are effective in a practical sense for this type of separation. It has heretofore been extremely difficult to isolate pure nonaromatic compounds from complex mixtures such as petroleum fractions. In accordance with the present invention, practical methods are provided whereby pure individual parafiins, pure individual naphthenes, pure individual olefins, or. pure individual alkaryl hydrocarbons may be recovered, i.e. separated from their position isomers. Thus, we may separate n-heptane from 2,4-dimethyl pentane, 2-methyl heptane from triptane (2,2,3,3- tetramethyl butane), dimethylcyclohexane from ethylcyclohexane, n-hexene-l from 4-methyl pentene-l, cumene from pseudocumene, etc. These separations, it will be observed, are between hydrocarbons which differ from each other primarily in the degree of branching of the alkyl groups, or more generally in the degree to which the carbon skeleton of the alkyl groups are exteriorly surrounded by hydrogen atoms. As between the chemical types involved, the parafi'ins are generally most soluble in the primary solvent, the naphthenes next, the olefins next, and the aromatics least soluble. This order of solubility is reversed in the secondary solvent.

- The order of solubility of hydrocarbons in the respective solvents is determined by their relative paraffinicity. The following hydrocarbon radicals contribute to increasing parafiinicity per carbon atom of radical, in the order named:

Aryl

Alkinyl Alkenyl Naphthenyl n-Alkyl Iso-Alkyl Methyl The above radicals thus also contribute, in the order named, to increasing solubility in the primary solvent, and to decreasing solubility in the secondary solvent. In estimating the overall paraffinicity of a given hydrocarbon, the presence or absence of the above radicals must be first considered, and then the relative proportion of the molecule made up by the respective radicals must also be considered. Obviously, no exact formula can be cited by which the paraifinicity factor, or index, of all the various hydrocarbons can be accuractely predicted. However, based on the above table of radicals, and the experimental data available, the following table of illustrative hydrocarbon types is cited, the types being listed in approximate order of decreasing paraflinicity, and intermediate types may be readily interpolated with approximate accuracy:

Highly branched paraflins Less highly branched paraffins n-Paraiiins of low molecular weight Highly poly-alkylated naphthenes n-Parafins of high molecular weight Mono-olefins highly branched near the double bond Naphthenes containing one or two large alkyl side chains Naphthenes containing one or two small alkyl side chains Pure naphthenes Mono-olefins highly branched remotely from the double bond Unbranched mono-olefins of high molecular Weight Unbranched mono-olefins of low molecular weight Alkenyl naphthenes Acetylenic hydrocarbons (alkynes) Polyolefins above diolefins .Highly alkylated aromatics 3 Less highly alkylated aromatics Naphthenyl aromatics Alkenyl aromatics Pure aromatics With any mixture of hydrocarbons, the members of which (1) contain a substantial alkyl substituent, (2) differ from each other in molecular weight by not more than about 25%, and (3) contain the same additional hydrocarbon radicals (e.g. vinyl, vinylidene, cyclohexyl, cyclopentyl, ethinyl, phenyl, etc.), a relative parafiinicity index for each member may be calculated by the formula:

where:

P=number of primary alkyl carbon atoms S=number ofsecondary alkyl carbon atoms T=number of tertiary alkyl carbon atoms Q=number of quaternary alkyl carbon atoms N =total number of alkyl carbon atoms The hydrocarbon with the highest paraflinicity index will in general be selectively dissolved by the primary solvent in preference to the others, and the hydrocarbon of lowest parafiinicity index by the secondary solvent. Intermediate members will have proportionate intermediate solubilities. Examples of hydrocarbon pairs which may be separated in accordance with this invention include the following:

Ethane; methane n-Butane; isobutane n-Butane; 2,2dimethylpropane Z-methyl butane; 2,2-dimethyl propane n-Pentane; 2-methyl butane n-Hexane; Z-methyl pentane Methyl pentane; 2,3dimethyl butane 2-methyl pentane; 2,2-dimethyl butane n-Heptane; Z-methyl hexane n-Octane; 2,2,3,3 tetramethyl butane Z-methyl heptane; 2,2,3,3-tetramethyl butane (12) 2,5-dimethyl hexane; 2,2,3,3-tetramethyl butane (13) 2,2,4-trimethyl pentane; 2,2,3,3-tetramethyl butane 14) n-Heptane; 2,2,3,3-tetramethyl butane (15) n-Decane; 2-methyl nonane (16) n-Dodecane; 2-methyl undecane (17) n-Octadecane; 2,2-dimethy-l hexadecane (l8) cyclohexane; methyl cyclopentane (19) Cyclohexane; 2,2-dimethyl pentane (20) Methyl cyclohexane; 1,2-dimethyl cyclopentane (21) Methyl cyclohexane; n-heptane (22) Methyl cyclohexane; 2-methyl hexane (23) Methyl cyclohexane; 2,2,4-trimethyl pentane (24) Ethyl cyclohexane; 1,3-dimethyl cyclohexane (25) Isopropyl cyclohexane; 1,2,4-trimethyl cyclohexane (26) Isopropyl cyclohexane; nonane (27) 2-pentene; 2-methyl bntene-l (28) 2-pentene; 2-methyl butene-Z (29) l-heptene; 2-methyl hexene-l (30) l-hexane; S-methyl hexene-l (31) 2,5-dimethyl hexene-3; 1,3-dimethyl cyclohexane (32) l-octene; n-octane (33) Toluene; methyl cyclohexane (34) Cumene; isopropyl cyclohexane (35) Cumene; pseudocumene (36) Cumene;mesitylene (37) o-Xylene; p-xylene (38) Ethylbenzene; m-xylene (39) S-methyl butyne-l; l-pentyne (40) l-octyne; 3-methyl heptyne-l The above examples are cited for purposes of illustration only, and the same principles may be utilized to resolve other mixtures, or more complex mixtures, either partially or completely.

pounds containing only carbon and fluorine, are operative azeotrope formers for separating straight-chain from branch-chain hydrocarbons (US. Patent 2,692,227). It is found however that azeotropic distillation is not as eflicient per theoretical stage as is the dual-solvent extraction of this invention. Furthermore, azeotropic distillation involves the use of perfluorocarbons which necessarily boil fairly close to the hydrocarbons being separated. The result is that inevitable iosses of solvent occur, and the perfluorocarbons are at present very expensive materials. Solvent extraction is inherently a more economical process than azeotropic distillation in regard to cost of equipment, heating expense and ease of control. Furthermore, solvent extraction is more flexible in that solvents boiling either above or below the boiling point of the mixture may be employed, and also mixed perfluorocarbons boiling over a wide range may be employed. Azeotropic distillation on the other hand requires a substantially pure perfluorocarbon having a fixed boiling point, and these are relatively expensive as compared to e.g. perfluorinated kerosene.

The perfluoro compounds employed herein may be either perfluorocarbons, or perfluoro-halocarbons wherein at least 90%, and preferable at least 95%, of the halogen atoms are fluorine atoms. Any remaining halogen atoms may be chlorine, bromine or iodine, but are preferably chlorine. The general requirement is that all hydrogen atoms be replaced by halogen atoms, at least 90% of which are fluorine. The preferred group comprises the 0 perfluorocarbons, which contain only carbon and fluorine.

It is known that the perfluorocarbons, i.e.those com- A wide'variety of perfluorocarbons are known, ranging from tetrafluoromethane, which is' a gas at normal pressures and temperature, through the entire aliphatic series up to compounds containing 20 or more carbon atoms. A wide variety ofperfluorinated naphthenie and aromatic compounds is also well known. Various methods for preparing such perfluorocarbons are described in- Industria-l and Engineering Chemistry, vol. 39,'pages 290- 421 (1947), and the physical properties of a wide variety of individual perfluorocarbons are set forth on pages 367 to 380 of said publication. The preparation and properties of other perfluorocarbons are described in US. Patent Nos.: 2,384,821; 2,404,374; 2,432,997; 2,436,142; 2,456,- 027; 2,456,028; 2,459,780; 2,459,783 and others. In addition to individual perfluorocarbons, complex mixtures of such compounds obtained by perfluorinating various petroleum fractions, e.g. kerosene, gas oil, lubricating oil, etc., have been prepared and are available commercially. As employed'herein, the term perfluorocarbon is meant to include any such individual compound or mixtures thereof.

Specific examples of suitable perfluorocarbons include perfluoropentane, perfluorohexane, perfluoromethylhexane, perfluorocyclopentane, perfluorocyclohexane, perfluoromethylcyclohexane, perfluoroheptane, perfluorotrimethylpentane, perfluorononane, perfluorodecane, perfluoroundecane, perfluorododecane, perfluorodimethylcyclohexane, perfluoroindane, perfiuorobenzene, perfluoroof about 1% to 20% byvo1ume at20" C. The solvent power may be increased twoto four-fold by substituting one chlorine atom in e.g. perfluoroheptane.

-It is preferred to employ a perfluoro compound with a boiling point which is substantially different from, i.e. either substantially above or substantially below, the boiling point of the feed mixture. Difierences in boiling point of 20 to 200 C. are preferred. By employing such solvents, an efiicient and complete separation of the solvent from the extracted hydrocarbon is readily achieved by distillation, and there is no problem of azeotrope formation.

The secondary solvent employed herein may be defined broadly as any polar organic compound, or compounds, which are substantially immiscible ;with the perfluoro compound at the extraction temperature, and which exhibit a preferential solvent action on hydrocarbons having a relatively high carbon/hydrogen ratio as compared to hydrocarbons having a relatively low carbon/ hydrogen ratio. This defines a well-recognized class of materials. Typical examples include nitro compounds, oxygenated and/or chlorinated compounds such as: phenol, cresylic acids, alkyl phenol mixtures, Carbitols (diethylene glycol mono ethers) such as methyl, ethyl, propyl Carbitols, chlorinated dialkyl ethers such as beta-beta-dichloroethyl ether, nitrobenzene, nitrotoluene, nitroxylenes, naphthols, alkyl naphthols, benzophenone, phenyl tolyl ketone, diphenylene ketone, alkyl phthalates, such as dimethyl phthalate, alkyl salicylates such as methyl salicylate, benzyl alcohol, benzyl chloride, benzo tri-chloride, diphenyl oxide, ditolyl oxide, tetra hydro furfuryl alcohol, furfuryl alcohol, furfural, the mono glycerol others such as l-methoxy glycerol, 2-methoxy glycerol, l-ethoxy glycerol, 2-ethoxy glycerol, l-propoxy glycerol, Z-propoxy glycerol, l-isopropoxy glycerol, 2-isopropoxy glycerol.

Aliphatic dinitriles may also be used, such as: malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitIile, oxydiacetonitrile, thiodiacetonitrile, iminodiacetonitrile, B,fi'-oxydipropionitrile, fl,,B'-thiodipropionitrile, fi,fi'-iminodipropionitrile.

Still other examples of suitable secondary solvents include mono nitriles such as: benzonitrile, p-ethyl benzonitrile, p-methoxy benzonitrile, phenoxy acetonitrile, phenyl mercapto acetonitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, cyclohexyl acetonitrile, ethoxy acetonitrile, S-methoxy propionitrile, isopropoxy acetonitrile, fi-isopropoxy propionitrile, methoxy acetonitrile, isopropyl mercapto acetonitrile, fi-(methyl mercapto) propionitrile, and the like. 7

Various amines may also be used, such as: triethylamine, N-butyl amine, N-hexyl amine, N-methyl, N- (n-butyl) amine, di-isopropyl amine, tri-isopropyl amine, N-ethyl, N,N-diisopropyl amine, N-ethyl, N-(methoxyethyl) amine, N,N-diethyl, N-(methoxyethyl) amine, N- isopropyl, N,N-di(methoxyethyl) amine, aniline, N,N-dimethyl aniline, N-isopropyl aniline, diphenyl amine, N- methyl cyclohexyl amine, piperidine, N-methyl piperidine, pyrrolidine, N-methyl pyrrolidine, N-isopropyl pyrroli dine, pyrrole, N-ethyl pyrrole, thiazole, tetrahydro thiazole, morpholine, N-methyl morpholine, N-ethyl morpholine, N-isopropyl morpholine, pyridine, chlorinated pyridines, nitro pyridine, hydroxy pyridine, quinoline, isoquinoline, S-nitro quinoline, 'y-picoline, B-picoline, ocpicoline, u-collidine, fl-collidine, 'y-collidine, 2,4-lutidine, 2,6-lutidine, 3,4-lutidine.

The foregoing secondary solvents are in general quite insoluble in the above-described primary solvents. Mutual solubilities of not more than 10% by volume, and usually less than 2% by volume, are found at room temperatures.

The relative amounts of primary and secondary solvent to be employed may vary over a wide range, depending upon the relative proportions of the hydrocarbons to be separated. From a broadly operative standpoint, the volume ratio of primary/secondary solvent may range anywhere between about 0.1 and 20, with the preferred ratios falling within the range of 0.5 to 5. In multi-stage extraction, maximum purity of a given feed component is obtained by employing relatively larger proportions of the solvent in which that component is least soluble. In general, the factors to consider in determining the ratio of primary/secondary solvent are (1) that sufiicient of each solvent should be used at least to dissolve the desired feed component, and (2) suflicient excess of one or the other should be used to give the desired purity.

The temperature at which the extraction is performed may vary over a wide range, from about 20 to 400 =C., but in most cases it will be found that ordinary atmospheric temperatures are adequae, e.g. from about 0 to 50 C. Where the particular solvents used exhibit an undesirably low solvent capacity, it will be preferable to use elevated temperatures, e.g. 50 to 200 C. The perfluorocarbons generally boil at a temperature lower than their parent hydrocarbon, and hence where lowboiling compounds are concerned, pressure vessels may be necessary at elevated temperatures.

In cases where the secondary solvent displays an undesirably high solvent capacity for the hydrocarbons, such solvents may be modified by the addition of other solvents or modifiers such as, for example, aliphatic alcohols, glycols, water and the like. Proportions of such modifiers ranging between about 0.5% and 20% by volume may be employed. The addition of water is particularly desirable in the case of solvents such as benzonitrile or morpholine, in which the hydrocarbons are quite soluble at room temperatures. Where the solvent capacity is too high, it is usually found that the selectivity is reduced.

The process may be practiced by any conventional method. For example, a series of batch extractions may be performed as follows: in the first stage, the two solvents are agitated with the hydrocarbon mixture to produce two immiscible phases; it is undesirable to use so much hydrocarbon as to produce a third phase at equilibrium. The two solvent phases thus formed are then separated, and the primary solvent extract is then again extracted with, preferably, a lesser quantity of the secondary solvent. The secondary solvent extract is extracted with a lesser quantity of the pure primary solvent. These repeated washings are then continued until each solvent phase contains its respective hydrocarbon in the desired purity. This procedure becomes analogous to continuous countercurrent extraction when the rafiinate from each successive washing of the primary or secondary solvent phase is used in the preceding washing stage.

It is ordinarily preferable however to employ continuous countercurrent extraction, as may be obtained by passing the solvents countercurrently to each other through an extraction column, and introducing the feed mixture at an intermediate point in the column. This procedure is illustrated more specifically in the drawing, which is a flow sheet representing one particular modification. It will be understood however that the invention is not restricted to this modification.

An original feed mixture consisting for example of a narrow-boiling heart-cut from a reformed gasoline fraction is brought in through line 1, and introduced near the bottom of an aromatics extraction column 2.. This feed will normally contain paraifins, aromatics, and a small proportion of naphthenes, and may boil for example between about and C. In aromatics extraction column 2, only one solvent is used, i.e. the secondary solvent of this invention, in order to strip out the aromatic hydrocarbons. This is a simple matter of economy in that the more expensive dual solvent extraction system is usually not required to obtain effective separation between aromatics and parafiinic or naphthenic hydrocarbons. However, the dual solvent system may be employed for that purpose if desired.

In the ease illustrated, the secondary solvent is introduced near the top of column 2 via line 3 and flows downwardly countercurrently to the feed. The aromatic extract is withdrawn through line 5 and transferred to a stripping column 6 wherein aromatic hydrocarbons are distilled overhead via line 7. The stripped solvent is withdrawn as bottoms via line 8 and is recycled to the column via line 3. 7 7

The non-aromatic raflinate from column 2 is withdrawn via line 10, and introduced near the mid-point of dual solvent extraction column 11 for separation of the non-aromatic components. In column 11, the primary solvent, which is usually the heavier of the two, is introduced at the top of column 11 via line 12 and flows downwardly countercurrently to the secondary solvent which is introduced near the bottom of the column via line'13. The feed to column 11 still contains a small amount ofwthe secondary solvent from column 2, and hence the amount of secondary solvent introduced through line 13 should be adjusted accordingly. The feed introduced to column 11 is ordinarily distributed in the column by means of a suitable liquid distributing ring 9, and the rate of introduction is such that the hydrocarbons go into solution substantially immediately. The upwardly flowing secondary solvent dissolves out the least paraflinic components, while the downwardly flowing primary solvent dissolves out the most paraflinic (i.e. most branched) components. Extraction column 11 may be of conventional design, e.g. it may be filled with suitable inert packing such as glass beads, raschig rings, porcelain chips, etc., to promote phase contact. Alternatively, and preferably, the column may be of the perforated plate type, whereby a greater number of theoretical extraction stages may be obtained per unit of column height. These types of columns are conventional and hence need not be described in detail.

The primary solvent extract is withdrawn from the bottom of column 11 via line 15, at a rate controlled by interface level controller 14, and sent to a stripping column 16 wherein the more highly paraflinic component is distilled overhead via line 17, and stripped primary solvent, containing a small proportion of the secondary solvent, is withdrawn as bottoms and recycled via line 19 and line '12 to the top of column 11.

The secondary solvent extract, containing the less Beta Mole ratio A /B in primary solvent phase Mole ratio A/B in secondary solvent phase when the two phases are at equilibrium. The Beta factor is hence a measure of the degree of separation which is obtained in each theoretical stage of the extraction. When the Beta factor is known for any given feed mixture and solvent pair, the appropriate solvent ratios, reflux ratios, and number of theoretical stages required for any desired degree of separation may be readily calculated by well-known methods. To illustrate the efiec tiveness of some of the solvent systems described herein, the following examples are cited which should not however be considered as limiting in scope.

EXAMPLES A mixture consisting of 50% by volume of n-heptane, and 50% of 2,4-dimethylpentane was prepared as feed. This mixture was then added gradually with shaking to various solvent pairs until a third phase began to form. The various mixtures were then allowed to settle, the phases were separated, washed with water and subjected to analysis to determine the distribution of hydrocarbons therein. The primary solvent employed in all cases was perfluorodimethylcyclohexane, which is a mixture of the 1,3- and the 1,4-isomers, sold under the trade name of FOX-327 by du Pont Company. Various secondary solvents were employed as indicated in the following table. The ratio of primary solvent to secondary solvent was approximately by volume in all cases except Exparaflinic component, is withdrawn as overflow from the 40 'Periment 2 wherein the ratio was 1/1.

Table 1 Analysis, Primary Analysis Secondary Secondary Solvent Phase Solvent Phase Beta 2 443M111 Expt. ESohienta1 1 mp oye 1111.2,4- 101.1107 1111.2,4- 1311.1107 2I4-DMPII1O1 DMP DMP Benzonitrile--. o. 49 0. 42 3. 45 3. 7s 1. 27 Morpholine--- 0. 73 0. e3 1. 26 1. 4s 1. 35 Furiural 0. 03 0. 0.86 1.08 1.43 Anilin 1.10 0.93 0.75 1.10 1.84

top of column 11 via line 20, at a rate controlled by liquid level controller 18, and sent to secondary solvent stripping column 21 wherein the less paraflinic components are distilled overhead via line 22. The stripped secondary solvent is then withdrawn as bottoms via line 24, and the major portion is recycled via lines 25 and 13 to the bottom of column .11. A smaller portion of the secondary solvent in line 24 may be diverted through line 27 and recycled via line 3 to the top of column 2 to make up for the solvent which is removed from column 2 in the non-aromatic ratfinate in line 10.

The degree of separation which is obtained in column 11 may be easily controlled by varying the relative ratios of primary to secondary solvent. By using large proportions of secondary solvent, pure individual paraifins may be recovered in the primary solvent; by using large relative proportions of primary solvent, pure individual hydrocarbons may be recovered in the secondary solvent. Alternatively, a portion of the hydrocarbon products in lines 17 and/ or 22 may be recycled to intermediate points in the column as reflux, as will be understood by those These experiments show that anilin in combination with the perfluorocarbon is exceptionally effective, while furfural, morpholine and benzonitrile are also very effective. The eflectiveness of morpholine and benzonitrile may be substantially increased by adding two to five percent of water to decrease the solvent capacity.

By subjecting either of the solvent phases to additional extraction'stages of redistribution of the hydrocarbons is obtained to re-establish approximately the same ratio defined by the respective Beta factor. This process may be repeated until substantially separation of the hydrocarbon is obtained.

The effectiveness of the primary solvent alone (perfluorodimethylcyclohexane) was also determined for the same feed mixture by shaking a quantity of the solvent with the feed until equilibrium was established. Analysis of the solvent phase and the rafiinate phase showed that the Beta factor was only 1.12. This clearly demonstrates that the primary solvent alone is relatively ineffective for separating isomeric parafiins.

The Beta factor for anilin alone was also determined by shaking a quantity of the feed mixture with pure anilin and analyzing the extract and raflinate. The Beta factor was found to be 1.23. These experiments demonstrate the synergetic effect which is obtained by employing the dual solvent system. Where both solvents were employed the Beta factor was 1.84, whereas the primary solvent alone gave a factor of only 1.12, and anilin alone of only 1.23.

When other solvent systems within the purview of this disclosure are substituted in the foregoing examples, substantially similar results are obtained. Similarly, when other feed mixtures within the purview of the disclosure are employed, proportional degrees of separation are achieved. In all cases, the dual solvent systems are found to give a much higher separation factor than would have been predicted on the basis of the effectiveness of the individual solvents alone.

It will hence be apparent that the invention herein described is a broadly applicable procedure effective for separating many and varied types of hydrocarbon mixtures. Where simple bi-component or tri-component mixtures are concerned, an effective separation of one or more of the single components may be achieved in a single extraction column. In other cases, where more complex mixtures are involved, it may be desirable to segregate the feed into two less complex mixtures in a first extraction column, and then complete the separation in a succeeding extraction column or columns. In still other cases, a complete separation of pure compounds may be undesired, in which case the extraction conditions are adjusted in accordance with known principles, and those described herein, to achieve whatever degree and type of separation is desired.

In some instances for example it is particularly desirable to separate naphthenes from like-boiling paraffins and this may be readily accomplished without effecting any substantial separation of paraffins from paraflins, or naphthenes from naphthenes. Where complex mixtures are concerned, it is usually preferable to employ relatively narrow-boiling-range mixtures, boiling over a range of not more than about 30 C. When wider boiling range fractions are used, it becomes increasingly difficult to obtain any desirable type of separation, due to the overlapping paraifinicity of the various naphthenes and parafiins involved.

The foregoing description is not intended to be limiting in scope except where expressly stated, and the true scope of the invention is intended to be measured by the terms of the following claims.

We claim:

1. A method for resolving a hydrocarbon mixture containing at least two close-boiling hydrocarbon components wherein said components: (1) are members of the same chemical class selected from the group consisting of paraifins, olefines, naphthenes and alkaryl hydrocarbons, (2) contain the same non-alkyl hydrocarbon radicals if any, (3) difier from each other in degree of branching of their respective alkyl groups, and (4) have substantially the same carbon/ hydrogen ratio, which comprises subjecting said mixture to solvent extraction in contact with a dual solvent system in which the primary solvent is a perfluoro-halocarbon wherein at least 90% of the halogen atoms are fluorine atoms, and the secondary solvent is a polar organic compound which: (1) is substantially immiscible with said primary solvent and (2) displays a selective solvent action for hydrocarbons having a relatively high carbon/hydrogen ratio as compared to hydrocarbons of lower carbon/hydrogen ratio, and recovering from the resulting primary solvent extract a hydrocarbon fraction relatively enriched in the original hydrocarbon component containing the most highly branched alkyl groups, and recovering from the resulting secondary solvent extract a hydrocarbon fraction relatively enriched in the original hydrocarbon containing the less highly branched alkyl groups.

2. A process as defined in claim 1 wherein said primary solvent is a perfluorocarbon.

3. A process as defined in claim 1 wherein said secondary solvent is aniline.

4. A process as defined in claim 1 wherein said secondary solvent is furfural.

5. A process as defined in claim 1 wherein said secondary solvent is morpholine.

6. A process as defined in claim 1 wherein said secondary solvent is benzonitrile.

7. A process as defined in claim 1 wherein said hydrocarbon components consist of close-boiling paraflins differing in the degree of branching.

8. A process as defined in claim 1 wherein said hydrocarbon components consist of alkyl naphthenes.

9. A process as defined in claim 1 wherein said hydrocarbon components consist of monoolefins.

10. A process as defined in claim 1 wherein said hydrocarbon components consist of alkaryl hydrocarbons.

11. A process as defined in claim 1 wherein said primary solvent is a perfluorocarbon, and said secondary solvent is an aromatic amine.

12. A process as defined in claim 1 wherein said primary solvent is a perfluorocarbon, and said secondary solvent is an aromatic nitrile.

13. A method for resolving a mixture of parafiin hydrocarbons differing in degree of chain branching to obtain a fraction rich in highly branched-chain parafiins and a fraction rich in relatively straight-chain parafiins, which comprises (1) establishing a dual-solvent extraction zone by flowing a primary solvent which is essentially a perfluorocarbon counter-currently to a stream of a secondary solvent which is a polar organic compound substantially immiscible with said primary solvent and which displays a selective solvent action for hydrocarbons of relatively high carbon/ hydrogen ratio as compared to hydrocarbons of lower carbon/hydrogen ratio, (2) introducing said hydrocarbon mixture at an intermediate point in said extraction Zone to contact said solvents, (3) removing a primary solvent extract from one end of said extraction zone and recovering said highly branched-chain parafiin fraction therefrom, (4) removing a secondary solvent extract from the other end of said extraction zone and recovering said relatively straight-chain parafiin fraction therefrom.

14. A process as defined in claim 13 wherein said secondary solvent is an aromatic amine.

15. A process as defined in claim 13 wherein said secondary solvent is an aromatic nitrile.

16. A method for resolving a naphtha reformate feedstock to obtain an aromatic hydrocarbon fraction, a fraction rich in highly branched-chain paraflins and a fraction rich in relatively straight-chain paraflins, which comprises (1) subjecting said feedstock to a first solvent extraction step by countercurrent contact with a secondary solvent hereinafter defined and recovering therefrom an aromatic extract and a paraffinic ratfinate containing a minor proportion of dissolved secondary solvent, (2) establishing a dual-solvent extraction zone by flowing a primary solvent which is essentially a perfluorocarbon countercurrently to a stream of a secondary solvent which is a polar organic compound substantially immiscible with said primary solvent and which displays a selective solvent action for hydrocarbons of relatively high carbon/ hydrogen ratio as compared to hydrocarbons of lower carbon/hydrogen ratio, (3) introducing said paraflinic raflinate at an intermediate point in said dual-solvent extraction Zone to contact said solvents, (4) removing a primary solvent extract from one end of said dual-solvent extraction zone and recovering said highly branchedchain paraffin fraction therefrom, (5) removing a secondary solvent extract from the other end of said dualsolvent extraction zone and recovering therefrom said relatively straight-chain parafiin fraction and stripped secondary solvent, (6) recovering from said aromatic References Cited in the file of this patent UNITED STATES PATENTS Francis et a1 Dec. 22, 1953 

1. A METHOD FOR RESOLVING A HYDROCARBON MIXTURE CONTAINING AT LEAST TWO CLOSE-BOILING HYDROCARBON COMNONENTS WHEREIN SAID COMPONENTS: (1) ARE MEMBERS OF THE SAME CHEMICAL CLASS SELECTED FROM THE GROUP CONSISTING OF PARAFFINS, OLEFINES, NAPTHENES AND ALKARYL HYDROCARBONS, (2) CONTAIN THE SAME NON-ALKYL HYDROCARBON RADICALS IF ANY, (3) DIFFER FROM EACH OTHER IN DEGREE OF BRANCHING OF THEIR RESPECTIVE ALKYL GROUPS, AND (4) HAVE SUBSTANTIALLY THE SAME CARBON/HYDROGEN RATIO, WHICH COMPRISES SUBJECTING SAID MIXTURE TO SOLVENT EXTRACTION IN CONTACT WIHT A DUAL SOLVENT SYSTEM IN WHICH THE PRIMARY SOLVENT IS A PERFLUORO-HALCARBON WHEREIN AT LEAST 90% OF THE HALOGEN ATOMS ARE FLUORINE ATOMS, AND THE SECONDARY SOLVENT IS A POLAR ORGANIC COMPOUND WHICH: (1) IS SUBSTANTIALLY IMMISCIBLE WITH SAID PRIMARY SOLVENT AND (2) DISPLAYS A SELECTIVE SOLVENT ACTION FOR HYDROCARBONS HAVING A RELATIVELY HIGH CARBON/HYDROGEN RATIO AS COMPARED TO HYDROCARBONS FOR LOWER CARBON/HYDROGEN RATIO, AND RECOVERING FROM THE RESULTING PRIMARY SOLVENT EXTRACT HYDROCARBON FRACTION RELATIVELY ENRICHED IN THE ORIGINAL HYDROCARBON COMPONENT CONTAINING THE MOST HIGHLY BRANCHED ALKYL GROUPS, AND RECOVERING FROM THE RESULTING SECONDARY SOLVENT EXTRACT A HYDROCARBON FRACTION RELATIVELY ENRICHED IN THE ORIGINAL HYDROCARBON CONTAINING THE LESS HIGHLY BRANCHED ALKYL GROUPS. 